The term chromatography embraces a family of closely related separation methods. The feature distinguishing chromatography from most other physical and chemical methods of separation is that two mutually immiscible phases are brought into contact wherein one phase is stationary and the other mobile. The sample mixture, introduced into the mobile phase, undergoes a series of interactions (partitions) many times before the stationary and mobile phases as it is being carried through the system by the mobile phase. Interactions exploit differences in the physical or chemical properties of the components in the sample. These differences govern the rate of migration of the individual components under the influence of a mobile phase moving through a column containing the stationary phase. Separated components emerge in the order of increasing interaction with the stationary phase. The least retarded component elutes first, the most strongly retained material elutes last. Separation is obtained when one component is retarded sufficiently to prevent overlap with the zone of an adjacent solute as sample components elute from the column.
One kind of chromatography which has become of increased interest for separation of proteins is hydrophobic interaction chromatography (HIC), which is based on difference in surface hydrophobicity. Proteins and peptides usually sequester hydrophobic amino acids in domains away from the surface of the molecule, but still usually have sufficient hydrophobic groups exposed to allow interaction with hydrophobic ligands attached to a stationary phase. An advantage of HIC is that elution conditions are mild, which is preserves biological activity. One kind of available HIC media is based on aromatic interaction mode, such as Phenyl Sepharose™ (Amersham Biosciences, Uppsala, Sweden). Such aromatic derivatised media can e.g. be prepared by immobilisation on an agarose base matrix of phenyl glycidyl ether under Lewis acid catalysis.
Another kind of available HIC media is based on aliphatic interaction mode, such as Butyl Sepharose™ (Amersham Biosciences, Uppsala, Sweden). Such aliphatic ligands can e.g. as well be prepared in a similar fashion as described above, but this time with the use of aliphatic glycidyl ether.
Another specific chromatographic method, which utilises hydrophobic interactions but often with a much more hydrophobic base matrix than the conventional HIC, is reverse phase chromatography (RPC). In RPC, the base matrices are also more flow resistant than in conventional HIC, which allows higher flow rates during separation. Elution in RPC is performed by use of an organic solvent. RPC media are also commercially available, e.g Source™ media (Amersham Biosciences, Uppsala, Sweden).
With the development of recombinant DNA technologies, proteins have become of increased interest and consequently the need of efficient methods for purification thereof has increased. Up to know, ion exchange has been the most prevalent chromatography method for protein purification. However, proteins are complex molecules that could provide a plurality of possible interaction with a stationary phase. There are however no available general separation media that utilises both the hydrophobicity of a protein and other interactions simultaneously. Accordingly, there is a need in this field of HIC media that are supplemented with groups that provides one or more additional interaction modes. Consequently, there is also a need of efficient methods for preparing such multimodal media for use in HIC and RPC.
Finally, Feist and Danna (“Sulfhydryl cellulose: A New Medium for Chromatography of Mercurated Polynucleotides”. Patricia L. Feist and Kathleen J. Danna, Biochemistry, 20(15), p. 4243-4246) have disclosed a process of preparing sulfhydryl cellulose, which process includes to mix amino ethyl cellulose with an N-acetylhomocysteine thiolactone. The concentration of active sulfhydryl groups is determined by reacting the sulfhydryl cellulose with Ellmans reagent.